Pistons modeled by potentials

In this article we consider a piston modelled by a potential in the presence of extra dimensions. We analyze the functional determinant and the Casimir effect for this configuration. In order to compute the determinant and Casimir force we employ the zeta function scheme. Essentially, the computation reduces to the analysis of the zeta function associated with a scalar field living on an interval $[0,L]$ in a background potential. Although, as a model for a piston, it seems reasonable to assume a potential having compact support within $[0,L]$, we provide a formalism that can be applied to any sufficiently smooth potential.Comment: 10 pages, LaTeX. A typo in eq. (3.5) has been corrected. In "Cosmology, Quantum Vacuum and Zeta Functions: In Honour of Emilio Elizalde", Eds. S.D. Odintsov, D. Saez-Gomez, and S. Xambo-Descamps. (Springer 2011) pp 31

Casting a wide net: use of diverse model organisms to advance toxicology

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hahn, M. E., & Sadler, K. C. Casting a wide net: use of diverse model organisms to advance toxicology. Disease Models & Mechanisms, 13, (2020): dmm.043844, doi: 10.1242/dmm.043844.Toxicology – the study of how chemicals interact with biological systems – has clear relevance to human health and disease. Persistent exposure to natural and synthetic chemicals is an unavoidable part of living on our planet; yet, we understand very little about the effects of exposure to the vast majority of chemicals. While epidemiological studies can provide strong statistical inference linking chemical exposure to disease, research in model systems is essential to elucidate the mechanisms of action and to predict outcomes. Most research in toxicology utilizes a handful of mammalian models that represent a few distinct branches of the evolutionary tree. This narrow focus constrains the understanding of chemical-induced disease processes and systems that have evolved in response to exposures. We advocate for casting a wider net in environmental toxicology research to utilize diverse model systems, including zebrafish, and perform more mechanistic studies of cellular responses to chemical exposures to shift the perception of toxicology as an applied science to that of a basic science. This more-inclusive perspective will enrich the field and should remain central to research on chemical-induced disease.K.C.S. acknowledges support from the National Institutes of Health (NIH)(5R01AA018886). M.E.H. acknowledges support from the National Institute ofEnvironmental Health Sciences (NIEHS) through the Boston University SuperfundResearch Program (P42ES007381) and the Woods Hole Center for Oceans andHuman Health (NIEHS grant P01ES028938 and National Science Foundation grantOCE-1840381)

Relaxation in yield stress systems through elastically interacting activated events

We study consequences of long-range elasticity in thermally assisted dynamics of yield stress materials. Within a two-dimensinal mesoscopic model we calculate the mean-square displacement and the dynamical structure factor for tracer particle trajectories. The ballistic regime at short time scales is associated with a compressed exponential decay in the dynamical structure factor, followed by a subdiffusive crossover prior to the onset of diffusion. We relate this crossover to spatiotemporal correlations and thus go beyond established mean field predictions.Comment: 5 pages, 2 figures, to appear in PR

Casimir piston for massless scalar fields in three dimensions

We study the Casimir piston for massless scalar fields obeying Dirichlet boundary conditions in a three dimensional cavity with sides of arbitrary lengths $a,b$ and $c$ where $a$ is the plate separation. We obtain an exact expression for the Casimir force on the piston valid for any values of the three lengths. As in the electromagnetic case with perfect conductor conditions, we find that the Casimir force is negative (attractive) regardless of the values of $a$, $b$ and $c$. Though cases exist where the interior contributes a positive (repulsive) Casimir force, the total Casimir force on the piston is negative when the exterior contribution is included. We also obtain an alternative expression for the Casimir force that is useful computationally when the plate separation $a$ is large.Comment: 19 pages,3 figures; references updated and typos fixed to match published versio

Incommensurate chirality density wave transition in a hybrid molecular framework

Using single-crystal X-ray diffraction we characterise the 235\,K incommensurate phase transition in the hybrid molecular framework tetraethylammonium silver(I) dicyanoargentate, [NEt$_4$]Ag$_3$(CN)$_4$. We demonstrate the transition to involve spontaneous resolution of chiral [NEt$_4$]$^+$ conformations, giving rise to a state in which molecular chirality is incommensurately modulated throughout the crystal lattice. We refer to this state as an incommensurate chirality density wave (XDW) phase, which represents a fundamentally new type of chiral symmetry breaking in the solid state. Drawing on parallels to the incommensurate ferroelectric transition of NaNO$_2$ we suggest the XDW state arises through coupling between acoustic (shear) and molecular rotoinversion modes. Such coupling is symmetry-forbidden at the Brillouin zone centre but symmetry-allowed for small but finite modulation vectors $\mathbf q=[0,0,q_z]^\ast$. The importance of long-wavelength chirality modulations in the physics of this hybrid framework may have implications for the generation of mesoscale chiral textures, as required for advanced photonic materials.Comment: 5 pages, 3 figure

Læringsaktiviteter og profesjonsorientering- et utviklingsarbeid i ny grunnskolelærerutdanning

Denne artikkelen har utgangspunkt i en studie knyttet til ulike arbeidsformer i faget pedagogikk og elevkunnskap i lærerutdanningen. Formålet med artikkelen er å drøfte hvordan studentaktive læringsformer kan gi ulike inntak til kunnskapsinnholdet i faget og bidra til profesjonsforståelse. Innledningsvis presenteres relevant forskning som belyser forhold mellom teori og praksis i profesjonsutdanninger. Deretter beskrives tre ulike arbeidsformer som studien har fokus på. Arbeidsformene gjennomføres i en klasse første studieår i den nye grunnskolelærerutdanningen for 5.–10. trinn. Studentenes erfaringer med arbeidsformene er dokumentert i vurderingslogger. I tillegg er det gjennomført dybdeintervju med et utvalg studenter. Analyse av data har utgangspunkt i Kvales fortolkings-kontekster: selvforståelse, kritisk (common sense) og teoretisk forståelse (Kvale, 2009)

The Devil is in the Details: A study of how Ancient Greek historian Thucydides’ greatest work, the History of the Peloponnesian War, changed historiography

Before the time of recorded history, how did people view historical events? Was it just a story that was told and past down with narrative embellishments? Or did they take a more factual approach? This essay will explore one such work of historiography that attempts to transcend history as a story, and more as a necessary combination of dry facts for future generations to use. Thucydides\u27 History of the Peloponnesian War endeavors to relay only the facts of what he thought would be one of the most influential wars in the history of his modern world